CVE-2021-46936

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2021-46936", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2024-02-25T13:45:52.720Z", "datePublished": "2024-02-27T09:44:02.758Z", "dateUpdated": "2026-08-05T08:45:10.624Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:45:10.624Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n BUG: unable to handle page fault for address: ffffde49a863de28\n PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0\n RIP: 0010:tw_timer_handler+0x20/0x40\n Call Trace:\n <IRQ>\n call_timer_fn+0x2b/0x120\n run_timer_softirq+0x1ef/0x450\n __do_softirq+0x10d/0x2b8\n irq_exit+0xc7/0xd0\n smp_apic_timer_interrupt+0x68/0x120\n apic_timer_interrupt+0xf/0x20\n\nThis issue was also reported since 2017 in the thread [1],\nunfortunately, the issue was still can be reproduced after fixing\nDCCP.\n\nThe ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net\nnamespace is destroyed since tcp_sk_ops is registered befrore\nipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops\nin the list of pernet_list. There will be a use-after-free on\nnet->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net\nif there are some inflight time-wait timers.\n\nThis bug is not introduced by commit f2bf415cfed7 (\"mib: add net to\nNET_ADD_STATS_BH\") since the net_statistics is a global variable\ninstead of dynamic allocation and freeing. Actually, commit\n61a7e26028b9 (\"mib: put net statistics on struct net\") introduces\nthe bug since it put net statistics on struct net and free it when\nnet namespace is destroyed.\n\nMoving init_ipv4_mibs() to the front of tcp_init() to fix this bug\nand replace pr_crit() with panic() since continuing is meaningless\nwhen init_ipv4_mibs() fails.\n\n[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1"}], "metrics": [{"cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH"}, "scenarios": [{"lang": "en", "value": "AV:L - The bug is triggered by destroying a network namespace while TCP TIME_WAIT timers remain armed, which requires local syscalls (clone/unshare, socket connect/close); a remote packet alone cannot tear down the netns or hit this teardown ordering.\nAC:L - An attacker fully controls both sides\u2014creating TIME_WAIT sockets (including short-timeout tw_kill paths) and destroying the netns\u2014so the race between ipv4_mib_exit_net freeing stats and tcp_sk_exit_batch purging timers is attacker-driven and has been reproduced in the wild and by syzkaller.\nPR:L - An unprivileged process can create a user+net namespace (CLONE_NEWUSER|CLONE_NEWNET), open loopback TCP connections that enter TIME_WAIT, and exit the netns; CAP_SYS_ADMIN inside the user namespace is sufficient and does not require host root.\nUI:N - Exploitation requires no victim action; the attacker creates the sockets and destroys the namespace themselves.\nS:U - Impact is confined to the host kernel\u2019s networking subsystem authority; this is a standard kernel UAF/privilege-escalation class bug, not a VM/IOMMU/sandbox boundary escape.\nC:H - This is a use-after-free on net->mib.net_statistics in tw_timer_handler; UAF of freed kernel heap/percpu memory can be leveraged for information disclosure once the object is reused.\nI:H - tw_timer_handler performs __NET_INC_STATS writes into the already-freed percpu MIB, yielding a memory-corruption write primitive that can be escalated via heap reuse to integrity compromise or code execution.\nA:H - The vulnerability causes a real-world kernel page-fault panic in softirq context (tw_timer_handler), so availability impact is a full kernel oops/panic."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/ipv4/af_inet.c"], "versions": [{"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "15579e1301f856ad9385d720c9267c11032a5022", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "e73164e89d1be561228a4534e1091369ee4ba41a", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "5c2fe20ad37ff56070ae0acb34152333976929b4", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "a8e1944b44f94f5c5f530e434c5eaee787254566", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "fe5838c22b986c1190f1dce9aa09bf6a491c1a69", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "2386e81a1d277f540e1285565c9d41d531bb69d4", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "08eacbd141e2495d2fcdde84358a06c4f95cbb13", "status": "affected", "versionType": "git"}, {"version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["net/ipv4/af_inet.c"], "versions": [{"version": "2.6.27", "status": "affected"}, {"version": "0", "lessThan": "2.6.27", "status": "unaffected", "versionType": "semver"}, {"version": "4.4.298", "lessThanOrEqual": "4.4.*", "status": "unaffected", "versionType": "semver"}, {"version": "4.9.296", "lessThanOrEqual": "4.9.*", "status": "unaffected", "versionType": "semver"}, {"version": "4.14.261", "lessThanOrEqual": "4.14.*", "status": "unaffected", "versionType": "semver"}, {"version": "4.19.224", "lessThanOrEqual": "4.19.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.4.170", "lessThanOrEqual": "5.4.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.10.90", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.15.13", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver"}, {"version": "5.16", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "4.4.298"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "4.9.296"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "4.14.261"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "4.19.224"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "5.4.170"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "5.10.90"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "5.15.13"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.27", "versionEndExcluding": "5.16"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022"}, {"url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a"}, {"url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4"}, {"url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566"}, {"url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69"}, {"url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4"}, {"url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13"}, {"url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0"}], "title": "net: fix use-after-free in tw_timer_handler", "x_generator": {"engine": "bippy-1.2.0"}}, "adp": [{"providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T05:17:42.878Z"}, "title": "CVE Program Container", "references": [{"url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0", "tags": ["x_transferred"]}]}, {"metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2021-46936", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2024-09-10T16:01:57.788399Z"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-09-11T17:33:18.637Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CVE Program Container", "references": [{"url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13", "tags": ["x_transferred"]}, {"url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0", "tags": ["x_transferred"]}], "providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T05:17:42.878Z"}}, {"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2021-46936", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2024-09-10T16:01:57.788399Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2024-09-11T12:42:16.064Z"}}], "cna": {"title": "net: fix use-after-free in tw_timer_handler", "metrics": [{"cvssV3_1": {"version": "3.1", "baseScore": 7.8, "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}, "scenarios": [{"lang": "en", "value": "AV:L - The bug is triggered by destroying a network namespace while TCP TIME_WAIT timers remain armed, which requires local syscalls (clone/unshare, socket connect/close); a remote packet alone cannot tear down the netns or hit this teardown ordering.\nAC:L - An attacker fully controls both sides\u2014creating TIME_WAIT sockets (including short-timeout tw_kill paths) and destroying the netns\u2014so the race between ipv4_mib_exit_net freeing stats and tcp_sk_exit_batch purging timers is attacker-driven and has been reproduced in the wild and by syzkaller.\nPR:L - An unprivileged process can create a user+net namespace (CLONE_NEWUSER|CLONE_NEWNET), open loopback TCP connections that enter TIME_WAIT, and exit the netns; CAP_SYS_ADMIN inside the user namespace is sufficient and does not require host root.\nUI:N - Exploitation requires no victim action; the attacker creates the sockets and destroys the namespace themselves.\nS:U - Impact is confined to the host kernel\u2019s networking subsystem authority; this is a standard kernel UAF/privilege-escalation class bug, not a VM/IOMMU/sandbox boundary escape.\nC:H - This is a use-after-free on net->mib.net_statistics in tw_timer_handler; UAF of freed kernel heap/percpu memory can be leveraged for information disclosure once the object is reused.\nI:H - tw_timer_handler performs __NET_INC_STATS writes into the already-freed percpu MIB, yielding a memory-corruption write primitive that can be escalated via heap reuse to integrity compromise or code execution.\nA:H - The vulnerability causes a real-world kernel page-fault panic in softirq context (tw_timer_handler), so availability impact is a full kernel oops/panic."}]}], "affected": [{"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "15579e1301f856ad9385d720c9267c11032a5022", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "e73164e89d1be561228a4534e1091369ee4ba41a", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "5c2fe20ad37ff56070ae0acb34152333976929b4", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "a8e1944b44f94f5c5f530e434c5eaee787254566", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "fe5838c22b986c1190f1dce9aa09bf6a491c1a69", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "2386e81a1d277f540e1285565c9d41d531bb69d4", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "08eacbd141e2495d2fcdde84358a06c4f95cbb13", "versionType": "git"}, {"status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "lessThan": "e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0", "versionType": "git"}], "programFiles": ["net/ipv4/af_inet.c"], "defaultStatus": "unaffected"}, {"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "2.6.27"}, {"status": "unaffected", "version": "0", "lessThan": "2.6.27", "versionType": "semver"}, {"status": "unaffected", "version": "4.4.298", "versionType": "semver", "lessThanOrEqual": "4.4.*"}, {"status": "unaffected", "version": "4.9.296", "versionType": "semver", "lessThanOrEqual": "4.9.*"}, {"status": "unaffected", "version": "4.14.261", "versionType": "semver", "lessThanOrEqual": "4.14.*"}, {"status": "unaffected", "version": "4.19.224", "versionType": "semver", "lessThanOrEqual": "4.19.*"}, {"status": "unaffected", "version": "5.4.170", "versionType": "semver", "lessThanOrEqual": "5.4.*"}, {"status": "unaffected", "version": "5.10.90", "versionType": "semver", "lessThanOrEqual": "5.10.*"}, {"status": "unaffected", "version": "5.15.13", "versionType": "semver", "lessThanOrEqual": "5.15.*"}, {"status": "unaffected", "version": "5.16", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*"}], "programFiles": ["net/ipv4/af_inet.c"], "defaultStatus": "affected"}], "references": [{"url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022"}, {"url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a"}, {"url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4"}, {"url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566"}, {"url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69"}, {"url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4"}, {"url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13"}, {"url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0"}], "x_generator": {"engine": "bippy-1.2.0"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n BUG: unable to handle page fault for address: ffffde49a863de28\n PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0\n RIP: 0010:tw_timer_handler+0x20/0x40\n Call Trace:\n <IRQ>\n call_timer_fn+0x2b/0x120\n run_timer_softirq+0x1ef/0x450\n __do_softirq+0x10d/0x2b8\n irq_exit+0xc7/0xd0\n smp_apic_timer_interrupt+0x68/0x120\n apic_timer_interrupt+0xf/0x20\n\nThis issue was also reported since 2017 in the thread [1],\nunfortunately, the issue was still can be reproduced after fixing\nDCCP.\n\nThe ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net\nnamespace is destroyed since tcp_sk_ops is registered befrore\nipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops\nin the list of pernet_list. There will be a use-after-free on\nnet->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net\nif there are some inflight time-wait timers.\n\nThis bug is not introduced by commit f2bf415cfed7 (\"mib: add net to\nNET_ADD_STATS_BH\") since the net_statistics is a global variable\ninstead of dynamic allocation and freeing. Actually, commit\n61a7e26028b9 (\"mib: put net statistics on struct net\") introduces\nthe bug since it put net statistics on struct net and free it when\nnet namespace is destroyed.\n\nMoving init_ipv4_mibs() to the front of tcp_init() to fix this bug\nand replace pr_crit() with panic() since continuing is meaningless\nwhen init_ipv4_mibs() fails.\n\n[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1"}], "cpeApplicability": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "4.4.298", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "4.9.296", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "4.14.261", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "4.19.224", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.4.170", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.10.90", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.15.13", "versionStartIncluding": "2.6.27"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "versionEndExcluding": "5.16", "versionStartIncluding": "2.6.27"}], "operator": "OR"}]}], "providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T08:45:10.624Z"}}}, "cveMetadata": {"cveId": "CVE-2021-46936", "state": "PUBLISHED", "dateUpdated": "2026-08-05T08:45:10.624Z", "dateReserved": "2024-02-25T13:45:52.720Z", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "datePublished": "2024-02-27T09:44:02.758Z", "assignerShortName": "Linux"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["net/ipv4/af_inet.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "15579e1301f856ad9385d720c9267c11032a5022", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "e73164e89d1be561228a4534e1091369ee4ba41a", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "5c2fe20ad37ff56070ae0acb34152333976929b4", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "a8e1944b44f94f5c5f530e434c5eaee787254566", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "fe5838c22b986c1190f1dce9aa09bf6a491c1a69", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "2386e81a1d277f540e1285565c9d41d531bb69d4", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "08eacbd141e2495d2fcdde84358a06c4f95cbb13", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}, {"lessThan": "e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0", "status": "affected", "version": "61a7e26028b94805fd686a6dc9dbd9941f8f19b0", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["net/ipv4/af_inet.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "2.6.27"}, {"lessThan": "2.6.27", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "4.4.*", "status": "unaffected", "version": "4.4.298", "versionType": "semver"}, {"lessThanOrEqual": "4.9.*", "status": "unaffected", "version": "4.9.296", "versionType": "semver"}, {"lessThanOrEqual": "4.14.*", "status": "unaffected", "version": "4.14.261", "versionType": "semver"}, {"lessThanOrEqual": "4.19.*", "status": "unaffected", "version": "4.19.224", "versionType": "semver"}, {"lessThanOrEqual": "5.4.*", "status": "unaffected", "version": "5.4.170", "versionType": "semver"}, {"lessThanOrEqual": "5.10.*", "status": "unaffected", "version": "5.10.90", "versionType": "semver"}, {"lessThanOrEqual": "5.15.*", "status": "unaffected", "version": "5.15.13", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "5.16", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "0B63EF4E-6C8F-4CCD-A30C-09E949BDD667", "versionEndExcluding": "4.4.298", "versionStartIncluding": "2.6.27", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "883CB22B-11DA-4D54-8121-3F5494EDBD4C", "versionEndExcluding": "4.9.296", "versionStartIncluding": "4.5.0", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "B5D4F856-5F69-4F4A-911F-50A21B9A68B6", "versionEndExcluding": "4.14.261", "versionStartIncluding": "4.10.0", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "B34A1353-506A-4AB9-87EC-CD50F09DFB8A", "versionEndExcluding": "4.19.224", "versionStartIncluding": "4.15.0", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "56D16FBB-453E-4316-A027-E517828203D7", "versionEndExcluding": "5.4.170", "versionStartIncluding": "4.20.0", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "C87FB3FD-3E74-4588-A1A4-B9BA8AE0C06B", "versionEndExcluding": "5.10.90", "versionStartIncluding": "5.5.0", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "083E0940-932B-447B-A6B2-677DAE27FD04", "versionEndExcluding": "5.15.13", "versionStartIncluding": "5.11.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix use-after-free in tw_timer_handler\n\nA real world panic issue was found as follow in Linux 5.4.\n\n BUG: unable to handle page fault for address: ffffde49a863de28\n PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0\n RIP: 0010:tw_timer_handler+0x20/0x40\n Call Trace:\n <IRQ>\n call_timer_fn+0x2b/0x120\n run_timer_softirq+0x1ef/0x450\n __do_softirq+0x10d/0x2b8\n irq_exit+0xc7/0xd0\n smp_apic_timer_interrupt+0x68/0x120\n apic_timer_interrupt+0xf/0x20\n\nThis issue was also reported since 2017 in the thread [1],\nunfortunately, the issue was still can be reproduced after fixing\nDCCP.\n\nThe ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net\nnamespace is destroyed since tcp_sk_ops is registered befrore\nipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops\nin the list of pernet_list. There will be a use-after-free on\nnet->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net\nif there are some inflight time-wait timers.\n\nThis bug is not introduced by commit f2bf415cfed7 (\"mib: add net to\nNET_ADD_STATS_BH\") since the net_statistics is a global variable\ninstead of dynamic allocation and freeing. Actually, commit\n61a7e26028b9 (\"mib: put net statistics on struct net\") introduces\nthe bug since it put net statistics on struct net and free it when\nnet namespace is destroyed.\n\nMoving init_ipv4_mibs() to the front of tcp_init() to fix this bug\nand replace pr_crit() with panic() since continuing is meaningless\nwhen init_ipv4_mibs() fails.\n\n[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1"}, {"lang": "es", "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: net: corrige use-after-free en tw_timer_handler Se encontr\u00f3 un problema de p\u00e1nico en el mundo real como se muestra a continuaci\u00f3n en Linux 5.4. ERROR: no se puede manejar el error de p\u00e1gina para la direcci\u00f3n: ffffde49a863de28 PGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0 RIP: 0010:tw_timer_handler+0x20/0x40 Seguimiento de llamadas: call_timer_fn+0x2b/ 0x120 run_timer_softirq+0x1ef/0x450 __do_softirq+0x10d/ 0x2b8 irq_exit+0xc7/0xd0 smp_apic_timer_interrupt+0x68/0x120 apic_timer_interrupt+0xf/0x20 Este problema tambi\u00e9n se inform\u00f3 desde 2017 en el hilo [1], desafortunadamente, el problema a\u00fan se puede reproducir despu\u00e9s de corregir DCCP. ipv4_mib_exit_net se llama antes de tcp_sk_exit_batch cuando se destruye un espacio de nombres de red, ya que tcp_sk_ops est\u00e1 registrado antes de ipv4_mib_ops, lo que significa que tcp_sk_ops est\u00e1 al frente de ipv4_mib_ops en la lista de pernet_list. Habr\u00e1 un use-after-free en net-&gt;mib.net_statistics en tw_timer_handler despu\u00e9s de ipv4_mib_exit_net si hay algunos temporizadores de espera a bordo. Este error no se introduce mediante la confirmaci\u00f3n f2bf415cfed7 (\"mib: add net to NET_ADD_STATS_BH\") ya que net_statistics es una variable global en lugar de una asignaci\u00f3n y liberaci\u00f3n din\u00e1micas. En realidad, la confirmaci\u00f3n 61a7e26028b9 (\"mib: poner estad\u00edsticas de red en struct net\") introduce el error ya que coloca estad\u00edsticas de red en struct net y las libera cuando se destruye el espacio de nombres de red. Mover init_ipv4_mibs() al frente de tcp_init() para corregir este error y reemplazar pr_crit() con p\u00e1nico() ya que continuar no tiene sentido cuando init_ipv4_mibs() falla. [1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1"}], "id": "CVE-2021-46936", "lastModified": "2026-08-04T10:16:37.640", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "nvd@nist.gov", "type": "Primary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2021-46936", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2024-09-10T16:01:57.788399Z", "version": "2.0.3"}}]}, "published": "2024-02-27T10:15:08.017", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/08eacbd141e2495d2fcdde84358a06c4f95cbb13"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/15579e1301f856ad9385d720c9267c11032a5022"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/2386e81a1d277f540e1285565c9d41d531bb69d4"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/5c2fe20ad37ff56070ae0acb34152333976929b4"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/a8e1944b44f94f5c5f530e434c5eaee787254566"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/e22e45fc9e41bf9fcc1e92cfb78eb92786728ef0"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/e73164e89d1be561228a4534e1091369ee4ba41a"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/fe5838c22b986c1190f1dce9aa09bf6a491c1a69"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: net: fix use-after-free in tw_timer_handler", "id": "2266443", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2266443"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.3", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H", "status": "draft"}, "cwe": "CWE-416", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nnet: fix use-after-free in tw_timer_handler\nA real world panic issue was found as follow in Linux 5.4.\nBUG: unable to handle page fault for address: ffffde49a863de28\nPGD 7e6fe62067 P4D 7e6fe62067 PUD 7e6fe63067 PMD f51e064067 PTE 0\nRIP: 0010:tw_timer_handler+0x20/0x40\nCall Trace:\n<IRQ>\ncall_timer_fn+0x2b/0x120\nrun_timer_softirq+0x1ef/0x450\n__do_softirq+0x10d/0x2b8\nirq_exit+0xc7/0xd0\nsmp_apic_timer_interrupt+0x68/0x120\napic_timer_interrupt+0xf/0x20\nThis issue was also reported since 2017 in the thread [1],\nunfortunately, the issue was still can be reproduced after fixing\nDCCP.\nThe ipv4_mib_exit_net is called before tcp_sk_exit_batch when a net\nnamespace is destroyed since tcp_sk_ops is registered befrore\nipv4_mib_ops, which means tcp_sk_ops is in the front of ipv4_mib_ops\nin the list of pernet_list. There will be a use-after-free on\nnet->mib.net_statistics in tw_timer_handler after ipv4_mib_exit_net\nif there are some inflight time-wait timers.\nThis bug is not introduced by commit f2bf415cfed7 (\"mib: add net to\nNET_ADD_STATS_BH\") since the net_statistics is a global variable\ninstead of dynamic allocation and freeing. Actually, commit\n61a7e26028b9 (\"mib: put net statistics on struct net\") introduces\nthe bug since it put net statistics on struct net and free it when\nnet namespace is destroyed.\nMoving init_ipv4_mibs() to the front of tcp_init() to fix this bug\nand replace pr_crit() with panic() since continuing is meaningless\nwhen init_ipv4_mibs() fails.\n[1] https://groups.google.com/g/syzkaller/c/p1tn-_Kc6l4/m/smuL_FMAAgAJ?pli=1"], "name": "CVE-2021-46936", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Out of support scope", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2024-02-27T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2021-46936\nhttps://nvd.nist.gov/vuln/detail/CVE-2021-46936\nhttps://lore.kernel.org/linux-cve-announce/2024022751-CVE-2021-46936-2f8a@gregkh/T/#u"], "statement": "Red Hat Enterprise Linux 8 and 9 are not affected by this vulnerability.", "threat_severity": "Moderate"}

{}